DE2906678A1 - METHOD AND DEVICE FOR BURNING AN ARTIFICIAL CARBON BODY, IN PARTICULAR AN ANODE FOR ALUMINUM MELT FLOW ELECTROLYSIS - Google Patents

Description

Annex to the patent application from - 4 - H 79/4 Klöckner-Humboldt-Deutz Gr / Wr

Corporation

dated Feb. 15, 1979

Method and device for burning a charcoal body, in particular an anode for aluminum melt-flow electrolysis

The invention relates to a method and a device for burning an artificial carbon body, in particular an anode for aluminum fused-salt electrolysis, whereby a preformed green molding is made by means of electrical resistance heating is heated.

The prior art includes several known methods of burning charcoal bodies. A distinction must be made between those artificial carbon bodies that are not subject to extreme requirements with regard to the lowest possible electrical resistance coefficient. These are usually subjected to a firing process at a maximum of 1,350 ° C., often referred to in the specialist field as "carbonization ^11. The invention relates to this category.

Artificial carbon body, which also has extremely low drag coefficients and / or / must have strength values are produced according to the so-called Acheson process, whereby these electrodes after the carbonization by means of direct electrical resistance heating at temperatures around

030036/0104

290667B

K H D - 5 - H 79/4

2.800 ⁰ C are burned. This process is usually referred to as "graphitization" in the specialist field.

For burning charcoal bodies, for example, the following are used different procedures used:

1. The moldings are used as so-called "green ⁰ briquettes in a gas-fired oven and slowly heated to extremely slowly up to temperatures from 750 to 1350 ⁰ C, for a time held at temperature long and · -. Cooled closing slow this in the professional world Process known as "bake" takes between 15 and 50 days.

2. Graphitization of "baked", that is, pre-burned, artificial carbon bodies according to the Acheson process by means of electrical resistance heating in a furnace, in which the charcoal moldings themselves are used as heating elements. Depending on the size of the shaped body to be produced, the Graphitization process between a few hours and several hours Days.

3. Burning of larger shaped charcoal bodies, for example for use in atomic energy reactors, by direct Resistance heating of the green bricks while at the same time

030036/0104

KHD

- 6 - ^H.

tiger application of high pressures, for example in the order of 150 to 350 bar and above, in a stable Press mold under a mechanical press, where relatively high heating rates are used. For example, in GB-PS 794,989, page 8, lines 52 to 54, heating rates between 2 and 1000 ° C / min specified. The actual heating rates are primarily dependent on the dimensions of the heated body.

A disadvantage of the known methods is felt that in the case of so-called "baking" in gas-fired ovens, a dwell time of up to 50 days results in uneconomical oven dimensions and heat losses and thus correspondingly high manufacturing costs. This method is proven but uneconomical.

The electrical resistance heating in a press mold under high pressures requires the use of extremely complex machines Pressing devices as well as pressure-resistant forms, and is therefore because of the expenditure on machines and costs, for example for the production of large burned carbon anodes for aluminum melt-flow electrolysis from economical Reasons not acceptable.

- 7 030036/0104

K HO - 7 - H 79A

The object of the invention is to provide an economical process for the production of large burned charcoal bodies, in particular of anodes for aluminum melt flow electrolysis, for example with single-piece weights between and 5000 kp available, with preformed green mold blocks with the highest possible heating rates be burned by means of electrical resistance heating. The use of external compressive forces should be avoided as far as possible.

The solution to the problem, whereby a preformed green molding is heated up by means of electrical resistance heating * succeeds according to the invention in that the supply of the current * heat to the molding is carried out from at least two circuits.

With the invention there is the advantage that the mass of the to be heated by applying several circuits Body is divided into several independently heated zones, eliminating the difficulty of which up to now has consisted in the fact that local fluctuations in the resistance, particularly in the case of large carbon moldings led to considerable local temperature differences in the heated material with only one single circuit, as mentioned, for example, in British Patent Specification No. 1,470,640 on page 1, lines 55-59.

- 8 030036/0104

KHD - 8 - H 79/4

So far, as experience has shown, such local temperature differences have resulted, depending on the size of the carbon body _? until the heated briquette breaks apart, but at least the formation of cracks, which called into question the intended use of the charcoal body. These difficulties in the electrical heating of large carbon bodies, which were previously regarded as insurmountable, are eliminated with the invention.

With the subdivision of the power supply during the burning process in at least two power and heating circuits and the resulting subdivision of the heated mass into one of the number The number of parallel heating zones corresponding to the applied circuits will reduce the non-uniformity of the heating Kept control.

Therefore, in an embodiment of the invention, it is further advantageously provided that the heating is carried out without use significant external compressive forces takes place.

With this measure there is the advantage of a considerable Reduction of costs as well as savings in machine effort. Overall, this increases the cost-effectiveness of the manufacturing process vastly improved.

In a further embodiment of the invention it is provided that the circuits are applied in parallel, these individually

- 9 Q30036 / 0104

KHD - 9 - H 79/4

and are preferably set independently of one another with respect to the values of voltage and / or current intensity. This measure has the advantage that the individual can be controlled independently in parallel with one another in one and the same Carbon body allows heated zones.

In an expedient embodiment of the method, it is also provided that that the setting values of a circuit are made to measure ™ if the setting values at least one additional circuit would be controlled. This has the advantage that locally so-called "outliers" can be avoided, for example, that the individual circuits in a certain Power, voltage or current strength relationship to one another to be controlled.

Another expedient embodiment of the invention provides that the setting values of a circuit in accordance with at least one local temperature value of the charcoal body can be regulated. This measure has the advantage that the emergence of locally different temperature zones in the burned charcoal body by appropriate control · and Regulatory action is prevented.

A further advantageous embodiment of the method according to the invention provides that the direction of the current flow

- 10 0 30036/0104

KHD - 10 - H 79/4

through the carbon body, the direction of application of the force used to compress the green carbon body and / or the force field is rectified. This measure is particularly useful when compressing a large green charcoal body by means of a vibrator is advantageous because it has been found that the direction of the The force field causing the compression has an effect orienting the drag coefficient of the mass in a certain direction evokes.

A better homogeneity of the tarpaulin drag coefficients and thus a more even heating process was observed when the power supply electrodes and thus the current flow were applied in the same direction in which the densification process in molding the green carbon body was done.

In the embodiment of the procedure, it is finally provided that that the preformed green molding without significant intermediate cooling, starting from the temperature resulting in the manufacturing process, is fired.

This has the advantage that the previous cooling process is avoided as well as the loss of the Cooling of expelled heat content. There are further advantages because the green molding at the time of Production has a temperature that is absolutely the same in all places due to the mixing process of the molded mass, and thus has ideal conditions for the start of the electrical burning process.

030036/0104

KHD H 79/4

A device for carrying out the method according to the invention is characterized by at least two circuits each with a pair of power supply electrodes.

One embodiment of the device provides that in the charcoal body Probes for measuring the temperature are arranged, preferably in each area of the charcoal body at least one probe is assigned between a pair of electrodes.

Finally, there is further appropriate training of the device according to the invention in the arrangement of one connected to the probes by control lines Control unit, which is assigned by means of the individual circuits Control organs, the heating power of these circuits preferably in accordance with the determined by the probes Regulates temperature values.

The invention is explained in more detail below with the aid of a schematic block diagram. The figure shows the charcoal molding 7 to be burned, on the end faces 8 and 9 of which a pair of electrodes 1, 1'j 2, 2 ^f ; 3, 3 '; 4, 4 ⁸ j 5, 5 ¹ ; and 6, 6 ^{1 are} applied. Here, the pair of electrodes 1, 1 ¹ to the circuit 10, the pair of electrodes 2, 2 'to the circuit 20 and so on connected so that each pair of electrodes 1, 1 · to 6, 6 ^f each an independent circuit 10, 20, 30 , 40, 50, 60 is assigned.

- 12 -

030036 / 01OA

2908678

KHD - 12 - H 79/4

It is indicated that the circuit 10 is connected to the winding 10 'of a transformer not shown in detail is connected, the circuit 20 to the winding 20 ', the circuit 30 to the winding 30', circuit 40 to the Winding 40 ', circuit 50 to winding 50 ·, circuit 60 to winding 60 '.

In the molded charcoal body 7, when it is heated, there is a plurality in parallel as a result of the power supply applied, independently acting and controllable circuits 10 to 60 a division into a number of parallel Heating zones 11, 12, 13 »14, 15, 16. For better illustration are the imaginary zones 11 to 16 belonging to the homogeneous charcoal body 7 by dashed lines A, B, C, D, E marked one below the other.

The numbers 71 to 76 are purely schematic temperature measuring probes indicated which are assigned to the individual zones 11 to 16. From these temperature measuring probes 71 to 76 lead Control lines 77, 78 to the regulating unit 80. A control line leads from each individual temperature measuring probe 71 to 76 77 to the control unit 80, of which, however, only the two control lines are representative for the sake of clarity 77 and 78 are shown in the block diagram.

- 13 -

030036/0104

. "■ '-. 29Q6678

KHD - 13 - H 79/4

The function of the control unit 80 is not the subject of Invention and is made for those familiar with control engineering A person skilled in the art is assumed to be known. For example, it compares an activated temperature setpoint with that of one Temperature probe 71 to 76 determines and generates the actual value at. Deviation from a control pulse with a control line 79 is switched to an actuator 81. Corresponding it is the function of the overall control scheme for the person skilled in the art It goes without saying that the other circuits 10, 20, 30, 50, 60 are assigned analog control devices, but they are are likewise not shown in the present figure for reasons of clarity.

The actuating device 81 is used in a manner known per se the current strength and / or the voltage of the regulated circuit 40 - and in an analogous manner with a correspondingly similar one Control device for the current strength and / or voltage of the other circuits - independently of one another, that is, for each circuit individual, adjusted.

However, it is not the object of the present invention to provide a control scheme for the parallel and individually controllable To represent and show circuits 10 to 60, as a corresponding method and a device for regulating for is assumed to be known to the person skilled in the art.

■ ·. ■ _ 14 -030036/0104

KHD - 14 - ^{H 79/4}

In addition, the invention is not tied solely to the exemplary embodiment shown. For example, the number the circuits in any way by at least two Circuits can be selected up to an unlimited number. Next, for example, is the way of Regulation as well as the design of corresponding devices at the discretion of the person skilled in the art.

All methods and devices carried out with it in this way however, fall under the invention if they satisfy one of the applicable patent claims.

0 30036/0104

Claims (12)

KHD H 79/4 claims 1. Method for burning an artificial charcoal body, in particular an anode for aluminum melt flow electrolysis, whereby a preformed green molding by means of electrical Resistance heating is heated, characterized in that that the supply of the current heat to the molding comes from at least two circuits » 2. The method according to claim 1, characterized in that the heating without the application of significant external pressure forces he follows. 3. The method according to claim T or 2, characterized in that that the circuits are applied in parallel to the molding «, 4. The method according to any one of claims 1 to 3, characterized in that that the circuits are individually and preferably independently of one another with respect to the values of voltage and / or current intensity can be adjusted. 5. The method according to any one of claims 1 to 4, characterized in that that the setting values of a circuit in accordance with the setting values of at least one other circuit be managed. ° - 2 030036/0104 KHD - 2 - H 79/4 6. The method according to any one of claims 1 to 4, characterized in that that the setting values of a circuit according to at least one local temperature value of the Charcoal body can be regulated. 7. The method according to any one of claims 1 to 6, characterized in that that the direction of the current flow through the carbon body during the compression of the green carbon body applied direction of attack of the force and / or the force field is rectified. 8. The method according to any one of claims T to 7, characterized in that that the preformed green molding is fired without significant intermediate cooling, based on the temperature resulting from the manufacturing process * 9. Application of the method according to one of claims 1 to carbon bodies with individual weights between 500 and 10,000 kp. 10. Device for performing the method according to one of claims 1 to 9, characterized by at least two circuits (10, 20, 30, 40, 50, 60) each with a pair of power supply electrodes (1, 1 ·} 2, 2 "; 3, 3 '; 4, 4"; 5, 5 ¹ ; 03003 6/0104 K H D - 3 - H 79/4 11. The device according to claim 10, characterized in that in the charcoal body (7) probes (71, 72, 73, 74, 75, 76) for measuring the temperature are arranged, preferably each area (11, 12, 13, 14, 15, 16) of the charcoal »- body (7) between a pair of electrodes (1.1 * to 6, 6 ') at least one probe (71 to 76) is assigned. 12. Device according to one of claims 10 or 11, gekenh * is characterized by a control unit (8θ) connected to the probes (71 to 76) by control lines (77, 78), which by means of the individual circuits (10, 10 '; 20, 20 '; 30, 30'; 40, 40 ¹ ; 50, 50 ') associated control elements (81) regulates the heating power of these circuits preferably in accordance with the temperature values determined by the probes (71 to 76). 0 3 0036/0104